The present invention relates to a muffler for damping the noise entailed by the emission of exhaust gases from an exhaust system of an internal combustion engine and, more particularly, to an improvement in a retainer for retaining a sound absorbing member in an absorbent type muffler. 2. Description of the Prior Art
Mufflers heretofore proposed for the absorption of noise which accompany gases emanating from an exhaust system of an automotive or like internal combustion engine include one which uses a sound absorbing member, or absorbent. This type of muffler, generally referred to as an absorbent type muffler, comprises a pipe perforated with numerous holes for the passage of the gases, and a pipe larger in diameter than the perforated pipe and receiving the latter in its bore. The tubular space defined between the inner and outer pipes is filled with a permeable and heat resisting absorbent such as glass wool, rock wool, slag wool, and asbestos fibers. That is, an absorbent shaped in a mat having a predetermined thickness is wound around the outer periphery of the perforated or inner pipe or, alternatively, an absorbent baked after addition of heat resisting binder is inserted into the tubular space between the inner and outer pipes.
The problem encountered with a prior art absorbent type muffler having the above construction is that the absorbent filled in the tubular space is apt to be scattered in pieces while the muffler is in use, significantly deteriorating the function and durability of the muffler. Possible causes of such scattering of the absorbent are uneven packing of the absorbent due to machining errors, irregular density of the packed absorbent, play developed by vibration in the absorbent in the tubular space, i.e., the resulting clearance which would allow a gaseous stream flowing therethrough to entrain the absorbent, and high-velocity exhaust flows which separate the absorbent into pieces to entrain them while flowing through the absorbent. When two or more of such causes combine together, they contribute a great deal to the deterioration of the muffler.